In recent years, there has been an improvement in efficiency of an LED (Light Emitting Diode). With the improvement, the LED has been widely applied to a backlight of a display device, and illumination devices as a light source consuming less energy than a light bulb or a fluorescent lamp. In such devices, energy efficiency is particularly important.
Here, the LED, particularly a gallium nitride LED, is easily broken down due to electrostatic discharge. That is, the LED has a low reverse withstand voltage. As a measure against such a problem, a technique of connecting a zener diode (ZD) in antiparallel with the LED has been disclosed (see Patent Literature 1, for example).
The arrangement employing the ZD protects the LED from an excess voltage by allowing (i) an excess current generated by a forward excess voltage to be bypassed due to a zener breakdown, and (ii) an excess current generated by a reverse excess voltage to be bypassed by using the ZD as a normal forward diode. Further, in a case where a forward voltage is applied to the LED, no current flows across the ZD, and no energy loss is generated. This is because the forward voltage applied to the LED is less than a zener breakdown voltage of the ZD.
However, the use of the ZD has disadvantages of: difficulty in manufacturing the ZD as compared with a resistor; a big burden of the provision of the ZD in accordance with the LED, or the like; low long-term reliability as compared with a resistor; high cost of components of the ZD.
Meanwhile, a technique of connecting resistors in parallel with the LED has been disclosed (see Patent Literatures 2 and 3, for example). According to the technique disclosed in Patent Literature 2, a plurality of LEDs are connected in series, and resistors are connected in parallel with the plurality of LEDs, respectively. In the arrangement, even if wire breakage occurs in any of the plurality of LEDs, the other LEDs would not be turned off. This is because each of the resistors functions as a bypass resistor. Further, Patent Literature 3 discloses a technique for arranging resistors in such an LED element set that a plurality of LEDs are provided in a single package. According to the technique, a plurality of variable resistors are connected in parallel with the plurality of LEDs, respectively, so that luminance of each of the plurality of LEDs can be adjusted. Furthermore, as an example of provision of the resistor connected to the LED, there has been a disclosure of a technique of providing a thick film resistor in an LED package (see Patent Literature 4, for example).